Spectacle lens edge grinding machine

ABSTRACT

A spectacle lens edge grinding machine includes a machine frame and at least one grinding wheel connected to the machine frame. A rotatable spectacle lens holding shaft is fastened to the machine frame. The spectacle lens holding shaft is at least radially displaceable relative to the grinding wheel. A spectacle lens is secured to the spectacle lens holding shaft for grinding with the grinding wheel. At least one abutment is provided for contacting a spectacle lens having been ground to have a desired spectacle lens contour. A transducer for measuring at least one actual value of the spectacle lens contour relative to the at least one abutment is provided. A computer for controlling the spectacle lens edge grinding machine is provided, wherein the computer includes a memory in which nominal values of the spectacle lens contour are stored. The computer compares the at least one actual value to the nominal values in order to determine a deviation from the nominal values. The memory stores a programmable threshold value for the deviation and the computer controls an additional grinding step when the deviation surpasses the threshold value.

BACKGROUND OF THE INVENTION

The invention relates to a spectacle lens edge grinding machine in whichin a pregrinding step the spectacle lens receives its circumferentialcontour, is subsequently subjected to a finishing step, especially afacet grinding step, the circumferential data of the circumferentiallyground lens is determined, input into a computer, and the radialmovement, and optionally the axial movement, of the spectacle lensrelative to the grinding wheel is computer-controlled with the aid ofthe circumferential data in an optionally subsequently performedcorrective grinding step with the aid of the peripheral data with thecomputer.

Such a device is disclosed in German Patent 40 12 660 of the assignee.In this device the data of the circumferential contour of the spectaclelens is determined and input into the computer during or aftercompletion of the fine-grinding step with a transducer, operatingcontactless and arranged in a housing of the spectacle lens edgegrinding machine. The determined actual values of the circumferentialcontour are compared within the computer with nominal values of thecircumferential contour stored therein, and reaching or surpassing of apredetermined permissible deviation is detected, whereby finishinggrinding is performed only upon surpassing the permissible deviationwith control based on the corrective values resulting from thisdeviation.

Even though the principle of determining the actual values of thecircumferential contour of form-ground spectacle lenses and the thusoptionally resulting corrective grinding have been proven successful, ithas been shown in practice that the contact-free operating transducersarranged within the housing are disadvantageously effected by theatmosphere present in the area of the spectacle lens within the housingof the spectacle lens edge grinding machine which atmosphere is loadedmore or less uniformly by splashing cooling media and abrasive grit, sothat it is required, when exact measuring results and exact grindingresults based thereon are to be achieved, to perform a frequentcleaning.

Upon grinding the V-shaped bevel of a spectacle lens wear of thegrinding wheel at the V-shaped bevel groove results which not onlyresults in an enlargement of the finish-ground spectacle lens, but alsoin an increase of the acute angle of the V-shaped bevel, i.e., aflattening of the bevel. The flattening of the V-shaped bevel can beaccepted to a certain extent, as long as the spectacle lens is securelyheld within the bevel groove of the respective spectacle frame. Thisrequires, however, that the circumferentially ground spectacle lens issubjected to a corrective grinding which takes into consideration theflattening of the bevel.

It is thus an object of the invention to overcome the disadvantages ofthe known spectacle lens edge grinding machines and to design thetransducer such that with a simple construction, independent of theatmosphere, the resulting soiling and optionally present deposits withinthe housing of the spectacle lens edge grinding machine, a sufficientlyexact measuring result can be obtained. Furthermore, the measuringresults should additionally take into consideration changes of theV-shaped bevel due to wear of the grinding wheel used for manufacturingthe V-shaped bevel.

SUMMARY OF THE INVENTION

Based on this object, it is suggested for the spectacle lens edgegrinding machine of the aforementioned kind that it comprise at leastone abutment cooperating in a contacting manner with thecircumferentially ground spectacle lens and a transduces for receivingat least one actual value of the circumferential contour with respect tothe abutment.

Accordingly, the spectacle lens edge grinding machine according to thepresent invention is primarily characterized by:

a machine frame;

at least one grinding wheel connected to the machine frame;

a rotatable spectacle lens holding shaft fastened to the machine frame,the spectacle lens holding shaft being at least radially displaceablerelative to the grinding wheel, wherein a spectacle lens is secured tothe spectacle lens holding shaft for grinding with the grinding wheel;

at least one abutment for contacting a spectacle lens having been groundto have a desired spectacle lens contour;

a transducer for measuring at least one actual value of the spectaclelens contour relative to the at least one abutment;

a computer for controlling the spectacle lens edge grinding machine,wherein the computer comprises a memory in which nominal values of thespectacle lens contour are stored;

wherein the computer compares the at least one actual value to thenominal values in order to determine a deviation from the nominalvalues; and

wherein the memory stores a programmable threshold value for thedeviation and wherein the computer controls an additional grinding stepwhen the deviation surpasses the threshold value.

Preferably, the abutment is a ring positioned laterally adjacent to theat least one grinding wheel so as to be stationary relative to thegrinding wheel, wherein the spectacle lens after grinding the spectaclelens contour is transferred from a position at the grinding wheel to aposition at the abutment. The ring is expediently comprised of ringsegments.

One of the rings is positioned on either side of the grinding wheel andthe rings comprise a sensing head for measuring a spatial curve of thespectacle lens contour.

The machine preferably further comprises a control device forcontrolling an axial position of the spectacle lens holding shafttogether with the spectacle lens relative to the grinding wheel as afunction of the spatial curve of the spectacle lens contour, wherein thecontrol device is also operative when the actual values are measured.

In another embodiment the machine further comprises a stationary splashguard enclosing tightly the at least one grinding wheel exclusive agrinding zone for grinding the spectacle lens, wherein the rings areconnected to the splash guard.

The at least one abutment is a sensing head comprising a wedge-shapedgroove for detecting a radial value of the spectacle lens, whereinlateral sides of the wedge-shaped groove are positioned at an acuteangle and wherein the acute angle is identical to a maximum acute angleof a V-shaped bevel of the spectacle lens.

The sensing head in addition to the wedge-shaped groove has a plane areafor determining at least one radial value of a tip of the V-shaped bevelof the spectacle lens.

The machine preferably further comprises a drive comprising anadjustable clutch for radially displacing the at least one grindingwheel relative to the spectacle lens holding shaft. It may furthercomprise a switching device acting on the clutch so as to reduce atransferred torque during measuring the actual value of the spectaclelens contour.

The machine may further comprise a compound slide rest connected to themachine frame, wherein the at least one grinding wheel with the driveare connected to the compound slide rest so as to be displaceablerelative to the spectacle lens holding shaft, wherein the transducermeasures a displacement of the compound slide rest within the machineframe relative to the spectacle lens contour.

The transducer is preferably a digital transducer.

This abutment can be connected fixedly or displaceably with respect tothe spectacle lens holding shaft and the spectacle lens to a machineframe of the spectacle lens edge grinding machine. The spectacle lens istransferred onto this abutment after its contour has beencircumferentially ground, and the radius of a predetermined associatedangle of at least one circumferential point of the spectacle lens withground circumferential contour is measured relative to the abutment.

In general, the abutment can be positioned at any desired locationwithin the housing of the spectacle lens edge grinding machine, however,must be accessible as an abutment for the circumferentially groundspectacle lens. An especially simple and preferred embodiment of theabutment results when it is comprised of narrow rings, respectively,ring segments arranged laterally to the grinding wheel, respectively,grinding wheels which are stationary relative to the grinding wheel andonto which the spectacle lens, after grinding of the circumferentialcontour, is transferred.

In order to take into account changes of the V-shaped bevel due to wearof the grinding wheel used for the manufacture of the V-shaped bevel inthe measuring results, the sensing head for measuring the radius valuemay have a wedge groove with a wedge angle that is identical to thepermissible maximum acute angle of the V-shaped bevel at the spectaclelens.

When the circumferentially ground spectacle lens is inserted into thewedge-shaped groove, a measured radius will depend solely on the radialwear of the grinding wheel as long as the angle of the V-shaped bevel ofthe circumferentially ground spectacle lens does not surpass the angleof the wedge-shaped groove at the sensing head. Until the two anglesbecome identical, it is sufficient to perform a corrective grinding stepthat corresponds to the linear deviation.

When the wear of the grinding wheel to be used for the facet grinding isso great that the angle of the V-shaped bevel is greater than the angleof the wedge-shaped groove at the sensing head, the spectacle lens to bemeasured with its V-shaped bevel can no longer be inserted completelyinto the wedge-shaped groove so that a greater deviation is measured asis associated with the linear diameter change of the grinding wheel. Inthis case, the spectacle lens edge grinding machine can stop thegrinding process and send a signal that provides information to theoperators with regard to the grinding wheel having to be adjusted,respectively, being no longer usable.

It can be especially easily detected whether the angle of the V-shapedbevel at the contour-ground spectacle lens has surpassed a predeterminedvalue when the sensing head, in addition to the wedge-shaped groove, hasa flat area for an unchanged position of the spectacle lens and when atleast a radius value of the tip of the V-shaped bevel at thewedge-shaped groove and a further radius value with respect to the flatarea is measured. From the difference of these two values in comparisonto the nominal value it can be determined easily whether the change isstill within permissible limits or not.

Advantageously, the grinding wheel(s) may be tightly enclosed by astationary splash guard with the exception of the grinding zone, and therings, respectively, ring segments can be arranged at the splash guard.

These rings, respectively, ring segments can be arranged preferably onboth sides of a pregrinding wheel and may be embodied as a sensing headfor determining the spatial curve of the circumferential of thespectacle lens. Such a device is disclosed in German Patent 38 42 601 ofthe assignee and serves to determine the front and back spatial curve ofthe circumferential contour of the form-ground spectacle lens as well asthe respective thickness of the lens. This is achieved by carrying outoscillating reciprocal movements of the spectacle lens holding shafttogether with the spectacle lens or of the grinding wheel together withthe sensing head relative to one another. This, on the one hand, servesto ensure a uniform wear of the pregrinding wheel and, on the otherhand, to measure the spatial curve and the lens thickness of theform-ground spectacle lens. In this manner the computer present withinthe device according to German Patent 38 42 601 can be used not only tochange the axial position of the spectacle lens holding shaft togetherwith the spectacle lens relative to the grinding wheel according to thespatial curve of the contour of the spectacle lens for a controlledgrinding of a V-shaped bevel, but also for determining the actual valuesof the circumferential contour by means of the rings, respectively, ringsegments. Thus, they can be embodied to be very narrow because, due tothe control of the axial position of the spectacle lens holding shafttogether with the spectacle lens relative to the grinding wheelaccording to the spatial curve of the contour of the spectacle lens,there is no danger that the spectacle lens, when measuring thecircumferential contour, leaves the area of the abutment and reaches thepregrinding disk or the finish-grinding disk or the intermediate spaces.

In order to prevent grinding traces on the rings, respectively, ringsegments and/or the circumferentially contour-ground spectacle lens anda thus resulting falsification of the measuring results, the contactingof the spectacle lens at the rings, respectively, ring segments can beeffected by a drive which comprises an adjustable clutch. Its clutchmoments can be changed in the sense of reduction during measuring theactual values of the circumferential contour with a switching device.

When the grinding wheel with its drive is connected to a compound sliderest so as to be displaceable relative to the spectacle lens holdingshaft rotatably supported at the machine frame, the transducer can bearranged such that it measures the displacement of the compound sliderest within the machine frame relative to the circumferential contour ofthe circumferentially contour-ground spectacle lens. Since the compoundslide rest within the machine frame is arranged external to a tank forreceiving cooling liquid and the abrasive grit, the transducer is notnegatively affected by the atmosphere present within the area of thegrinding wheels and the spectacle lens to be ground.

Analogously, the transducer can be arranged relative to the spectaclelens holding shaft when the latter is axially and radially movablysupported at the machine frame relative to the rotating grinding wheelsin order to measure the actual values of the circumferential contour.

Preferably, a digital transducer can be used wherein the measured valuesare directly input to the computer and processed therein.

The present invention also relates to a method for grinding the edge ofa spectacle lens with a spectacle lens edge grinding machine, the methodcomprising the steps of:

a) measuring at least one actual radius of a predetermined angle at aperipheral point of a spectacle lens, ground to have a spectacle lenscontour, relative to an abutment;

b) inputting the at least one measured actual radius into a computerwith a memory;

c) comparing the at least one measured actual radius with acorresponding nominal radius stored in the memory of the computer todetermine a deviation from the nominal radius;

d) comparing the deviation to a threshold value stored in the memory ofthe computer; and

e) controlling with the computer an additional grinding step, when thedeviation surpasses the threshold value, for correcting the spectaclelens contour in order to compensate for the deviation.

Preferably, in the step a) the actual radius is a radius of acircumferential V-shaped bevel of the spectacle lens and is measuredrelative to a wedge-shaped groove of the abutment.

In the step a) the actual radius is additionally measured relative to aplane area provided at the abutment. The method further includes thestep of comparing the measured values measured relative to thewedge-shaped groove and relative to the plane surface in order todetermine whether a correction of the deviation of the actual radius,measured relative to the wedge-shaped groove, is possible.

Advantageously, in the step a) the actual radii of the entire spectaclelens contour are measured, wherein in the step c) the actual radii arecompared to the stored nominal radii of the entire spectacle lenscontour to determine the deviations from the nominal radii. The methodfurther includes the step of signalling the deviations when thedeviations surpass the threshold value, and the step of averaging thedeviations so as to perform the step e) according to the averageddeviation.

Preferably, in the step a) the actual radii of the entire spectacle lenscontour are measured. In the step c) the actual radii are compared tothe stored nominal radii of the entire spectacle lens contour todetermine the deviations from the nominal radii, and in the step e) onlysuch areas of the spectacle lens contour are corrected in which thedeviations surpass the threshold value.

The step a) includes the step of rotating the spectacle lens at a rpmhigher than the rpm for grinding the spectacle lens.

The inventive method for grinding the edges of spectacle lenses with theaforedescribed spectacle lens edge grinding machine can preferably becomprised of the steps of measuring the radius of a predeterminedassociated angle of at least one circumferential point of thecircumferential contour of the form-ground spectacle lens with respectto an abutment, inputting the measured value into the computer,comparing it to a stored nominal value, and, upon surpassing a storedpermissible deviation of the actual value with respect to the nominalvalue, performing an additional grinding process of the circumferentialcontour with a corresponding correction based on the deviation.

Preferably, the radius of at least one circumferential point of theV-shaped bevel of the circumferentially ground spectacle lens withrespect to a wedge-shaped groove at the abutment can be measured, sothat it is recognizable whether the angle of the V-shaped bevel is stillwithin the range of permissible values. In this scenario, with anadditional grinding process of the circumferential contour with acorrection corresponding to the deviation a still usable spectacle lenscan be produced.

When the angle of the V-shaped bevel of the circumferentiallycontour-ground spectacle lens is greater than the angle of thewedge-shaped groove, this means, that the grinding wheel which has beenused for grinding the V-shaped bevel must be adjusted, respectively, hasbecome unusable. This is indicated by the machine with a respectivesignal.

When the radius of at least one circumferential point of the V-shapedbevel of the circumferentially contour-ground spectacle lens is measuredrelative to the wedge-shaped groove at the abutment as well as relativeto the plane area of the abutment, it can be determined in a simplemanner by comparing these measured values whether a correction of thedeviation of the actual value from the nominal value, measured withrespect to the wedge-shaped groove, is still possible, respectively,whether the spectacle lens must be reground with a new or adjustedgrinding wheel.

When only one circumferential point is measured, the correction of theentire circumferential contour is based on the deviation measured atthis point. When this deviation results only from wear of thepregrinding wheel or of the finish-grinding wheel, which, in general, isuniformly distributed over the circumference, a sufficiently exactcircumferentially contour-ground spectacle lens can be manufactured withthis correction whose size is precise enough to be directly insertedinto a certain spectacle frame.

Since the deviations about the circumferential contour may vary, wherebythese deviations are determined by the shape of the spectacle lens andthe spatial curve of the circumferential contour, a greater precision ofthe corrective grinding step can be achieved when the entirecircumferential contour is measured, the values compared to the storednominal values, upon surpassing the threshold value of the permissibledeviation of the actual value relative to the nominal value the measureddeviations are averaged by the computer, and the additional grindingprocess of the circumferential contour is performed corresponding to theaveraged values. In all cases, a corrective grinding step is performedin order to maintain the actual value of the circumferential values at0:0.3 mm relative to the nominal values.

An even more precise correction of the circumferential contour can beachieved when the entire circumferential contour is measured, comparedto the stored nominal values, and, when locally deviations of the actualvalue with respect to the nominal values surpass the permissibledeviation, an additional grinding process is carried out only in areasthat have an impermissible deviation of the circumferential contour.

In order not to lose too much time for measuring the entirecircumferential contour of a formground spectacle lens, this measuringstep can be performed at rpm of the spectacle lens holding shaft thatare higher than the conventional rpm during the grinding process.

The inventive correction of the circumferential contour of the spectaclelens can be performed with spectacle lens edge grinding machines inwhich the contour of the spectacle lens is predetermined by a template.This template is connected to the spectacle lens holding shaft and restson an adjustable abutment that can be inventively adjusted by thecomputer for a corrective grinding step as disclosed above. In such aspectacle lens edge grinding machine the computer serves only to controlthe relative axial displacement of the grinding wheel and thecircumferentially contour-ground spectacle lens during grinding of afacet, the measuring of the circumferential contour, and optionally therequired corrective grinding step.

It is also possible to input into the computer the circumferentialcontour of a spectacle lens to be ground in the form of a set of data.In this case the template corresponding to the contour of the spectaclelens can be replaced by a circular disk and the movement of the abutmentis controlled by the computer which movement determines the contour ofthe spectacle lens to be ground.

Finally, it is also possible to control the relative distance betweenthe spectacle lens holding shaft and the grinding wheel directly by thecomputer, for example, with a compound slide rest which supports thegrinding wheels and which has a corresponding drive. In this case, theinventive correction of the circumferential contour grinding step canalso be performed in the aforementioned manner.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail in the following with the aidof the embodiment represented in the drawings. The drawings show in:

FIG. 1 a schematic side view of a spectacle lens edge grinding machinewith representation of the inventive abutment and transducer;

FIG. 2 a perspective representation of a splash guard enclosing twogrinding wheels with abutments in the form of ring segments and aspectacle lens holding shaft arranged in front thereof with a lens thathas been circumferentially ground;

FIG. 3 a representation of a detail measuring at least one radius of thecircumferentially ground spectacle lens with a V-shaped bevel groundwith a new grinding wheel;

FIG. 4 a representation similar to FIG. 3 in which the bevel has beenground with a grinding wheel that is worn pasta permissible limit;

FIG. 5 a representation according to FIG. 3 in which the V-shaped bevelproduced with a greatly worn grinding wheel is already so flat that thespectacle lens can no longer be inserted into a spectacle frame;

FIG. 6 a representation of measuring the radius of a circumferentiallycontour-ground spectacle lens in which the tip of the V-shaped bevel isplaced onto the flat portion of the sensing head; and

FIG. 7 an enlarged representation of a facet groove in a grinding wheelin a new and various worn states.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A compound slide rest 2 is connected to a machine frame 1 and has acarriage part 3 with guide rods 4 which are supported in bores 5 ofprojections 6 of a carriage part 7 so as to be displaceable radiallyrelative to the lens holding shaft 14 with a spectacle lens 24 securedthereat.

The carriage part 7 is arranged via guide tracks 8 at the machine frame1 so as to be displaceable in a direction parallel to the lens holdingshaft 14 and a shaft 10 for the pregrinding wheel 11 and a finishingand/or facet grinding disk 12 arranged coaxially thereto and having afacet groove 33.

The shaft 10 is supported with bearing supports 9 at the carriage part3. The grinding wheels 11, 12 and the spectacle lens 24 with the shafts10, 14 are surrounded by a housing 13 that at its bottom part comprisesa tank (not represented in detail) which prevents that cooling liquidand abrasive grit can enter the area of the compound slide rest 2.

An angle transducer 15 is connected to the spectacle lens holding shaft14 and to a computer 16.

A transducer 17 is arranged at the carriage part 7 and detects theradial displacement of the carriage part 3 relative to the spectaclelens holding shaft 14. This transducer 17 is also connected to thecomputer 16.

The radial displacement of the carriage part 3 is effected by a drivemotor 18 which is controlled via the computer 16 and control lines 21.The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.drive motor 18 is in driving connection with guide rods 4 via anelectromagnetic clutch 19.

In a nominal value memory 20 the circumferential contour values fordifferent spectacle lens shapes are saved in the form of polarcoordinates.

For grinding a preselected circumferential contour of a spectacle lens,a lens blank is clamped into the spectacle lens holding shaft 14 and iscontacted with the pregrinding disk 11. The resulting contact pressuredepends on the adjustment of the electromagnetic clutch 19 and isadjustable to different values for spectacle lenses made of plastic orsilicate glass as well as with respect to the optical values of thespectacle lens such as thickness of the edge of the spectacle lens.

The spectacle glass 24 is rotated in a manner known per se by the shaft14 whereby the velocity of rotation is conventionally 10 to 13 rpm. Theangular transducer 15 transmits to the computer 16 at identical angulardistances, for example, in increments of 6°, an impulse so that thecomputer 16 adjusts the respective radius of the spectacle lens via thedrive motor 18. During grinding of the circumferential contour of thespectacle lens 24 with the pregrinding wheel 11 the carriage part 7 andthus the grinding wheel 11 is in an oscillating movement parallel to theaxis of rotation of the spectacle lens 24 which is always switched atthe edge of the pregrinding wheel 11 to move in the opposite direction.This movement is controlled by a non-represented drive for the carriagepart 7 which is also connected to the computer 16. On both sides of thepregrinding wheel 11 ring segments 23 are arranged which are connectedto a splash guard 22 which is open within the contact area with thespectacle lens 24 and which encloses tightly the pregrinding wheel 11and the finish-grinding wheel 12. The ring segments 23 serve as asensing head and are connected with the sensor 26 which is schematicallyrepresented in FIG. 2. The sensor itself is connected with a controlline 27 to the computer 16. The oscillating movement of the carriagepart 7 and thus of the grinding disks 11, 12 and the splash guard 22enclosing them are controlled in a manner disclosed in German Patent 3842 601 by the sensor 26 and serve simultaneously to measure thecircumferentially contour-ground spectacle lens 24 with respect to thespatial curve of the front and backside as well as the thickness of theglass. These measured values serve to grind with the facet groove 33 atthe finish-grinding wheel 12 a bevel at the circumferentiallycontour-ground spectacle lens the course of which can be controlled bythe computer 16.

After having ground with the pregrinding disk 11 the contour of thespectacle lens according to the representation in FIG. 1, the spectaclelens 24 is automatically transferred onto the finishing grinding wheel12 and is precisely positioned relative to the facet groove 33. Thespectacle lens 24 is provided with a sufficient material tolerance forcarrying out the finish-grinding step.

After the finish-grinding step, the spectacle lens 24 controlled by thecomputer 16 is positioned precisely on the ring segments 23. The ringsegment 23 serves as an abutment for measuring the distance between thespectacle lens holding shaft 14 and this ring segment 23. Which point ofthe spectacle lens 24 is to be placed onto the ring segment 23 isdetermined by the computer 16 pursuant to input commands. In thesimplest case, it is sufficient that a single distance measurement isperformed, for this point the deviation of the actual value to therespective nominal value saved within the nominal value memory 20 isdetermined, and, upon surpassing a preset deviation, a further finegrinding step with correction of these deviations is controlled by thecomputer. This method based on measuring only one value assumes that thedeviations are substantially identical over the entire circumferentialcontour.

More precise is a measurement when the entire contour of the spectaclelens 24 is measured for a complete rotation of the spectacle lens 24while resting at the ring segment 23. Since the ring segments 23 arevery narrow in order to provide for a short axial extension of thegrinding disks 11, 12 within the splash guard 22, the computer 16imparts a movement to the carriage part 7 parallel to the axis of theshaft 14 which movement takes into consideration the spatial curve ofthe contour of the spectacle lens, respectively, of the bevel, so thatthe spectacle lens 24 during this one rotation for measuring thecircumferential contour remains on the ring segment 23. The distancevalues of the spectacle glass 24 are detected with the transducer 17 andsent to the computer 16 where a comparison with the nominal values takesplace.

When based on the comparison of the actual values with the nominalvalues an impermissible deviation of the contour of the spectacle lensresults, the computer 16 can then average the deviations over thecircumference and provide for a correction based on this average value,or the deviations are recorded point by point, compared with thecorresponding nominal values, and a corrective grinding step isperformed only where actually a deviation has been detected.

When the measurement is performed exclusively such that thecircumferentially ground spectacle glass is placed with its V-shapedbevel onto a flat area of the ring segment 23, it is possible to detectonly a deviation in the diameter of the grinding disk 23 and tooptionally correct it.

In FIGS. 3 to 7 it is shown that wear of the facet groove 33 of agrinding disk 12 not only results in a diameter change but also in anangle change of the V-shaped bevel.

In FIG. 7 a finish-grinding wheel 12 is represented with a facet groove33 in solid lines which has an angle ρ₁ which is smaller than theconventional angle of the facet groove within a spectacle frame. Aprecisely contour-ground spectacle lens can thus be inserted withoutproblems in a corresponding spectacle frame and rests with the tip ofthe bevel at the base of the facet within the spectacle frame.

FIG. 3 shows this state with respect to the wedge-shaped groove 28within the ring segment 23. This wedge-shaped groove 28 has an angle ρ₀which is greater than the angle ρ₁ of the facet groove 33 within thefinish-grinding wheel 12 and is substantially identical to the angle ofthe facet groove in conventional spectacle frames.

When a circumferentially contour-ground spectacle lens 24 with itsV-shaped bevel 30 is inserted into the wedge-shaped groove 28 of thering segment 23, the radius R₁ can be determined for this point. Whenthis measured radius R₁ deviates from a preset nominal value and is toogreat, the spectacle lens 24 is automatically returned to the finishinggrinding wheel 12 and a corrective grinding step is performed. In thecourse of time, the facet groove within the finish-grinding wheel 12will wear and will assume the shape shown with cross-hatched andidentified with reference numeral 34 in FIG. 7. The angle of this facetgroove of a worn finish grinding wheel 12 is identified with ρ₂. It isshown that simultaneously the depth of the facet groove 34 has increasedby the amount Δ₁. When a contour-ground spectacle lens 24 with aV-shaped bevel having an angle ρ₂ is inserted according to FIG. 4 intothe wedge-shaped groove 28 of the annular segment 23, a measured radiusR₂ results which is greater by the amount Δ₁ than R₁. In this case, acorrective grinding step can still be performed which will reduce thesize of the contour-ground spectacle lens 24 by the value Δ₁.

When the finishing grinding wheel 12 is worn down to such an extent thatthe facet groove 35 has the angle ρ₃, to which corresponds anenlargement of the depth having the value Δ₂, this flattened V-shapedbevel with the angle ρ₃ can no longer be completely introduced into thewedge-shaped groove 28 at the ring segment 23 but rests with itsflanges, as shown in FIG. 5, at the external edges of the wedge-shapedgroove 28. In this case, a radius R₁ is measured which, with respect toR₁, is not greater by the value Δ₂ but by a much greater value which isa function of this angle ρ₃. The computer 16 can be programmed such thatthe limit between the radius R₂ and the radius R₃ is detected and asignal released which shows the operator that the finish-grinding wheel12 is worn to such an extent that a corrective grinding step can nolonger be performed.

This limit can be determined easily when, as shown in FIG. 6, aftermeasurement of the radii R₁, R₂, respectively, R₁ with respect to thewedge-shaped groove 28 a further radius R₄ is measured such that thecircumferentially contour-ground spectacle lens 24 with its V-shapedbevel 30, 31, 32 is placed onto a flat area 29 of the annular segment23. From the difference of the radii R₁, R₂, respectively, R₃ to theradius R₄ a value results directly which is greater than zero when ρ₃>ρ₀. This is a measured value for which causes the computer to releasethe aforementioned signal that a corrective grinding step is no longerpossible and that the finish-grinding wheel must be exchanged oradjusted.

The comparative measurement must be performed only relative to theradius of the contour-ground spectacle lens 24 while for a more precisecorrective grinding step a measurement of the entire circumference ofthe spectacle lens 24 within the wedge-shaped groove 28 or on theflattened portion 29 of the ring segment 23 must be carried out.

The inventive device and the method are suitable to be used with fullyautomated, CNC-controlled spectacle lens edge grinding machines. Inthese spectacle lens edge grinding machines the stored nominal values ofthe circumferential contour serve to control the compound slide restcarrying the grinding wheels 11 and 12 such that directly the requiredcircumferential contour of the spectacle lens is produced.

The inventive method and the device are also suitable to be used withspectacle lens edge grinding machines in which the computer only servesto compare the actual values of the form-ground spectacle lens 24 withthe stored nominal values of the circumferential contour and to performa corrective grinding step while the actual form-grinding step of thespectacle lens is controlled by a template with the shape of thespectacle lens to be ground which is placed onto the spectacle lensholding shaft 14. The template rests in this case in a manner known perse at the abutment which is connected to the carriage part 3 and whicheffects the displacement of the grinding wheels 11, 12 and of thecarriage part 3. For performing a corrective grinding step the abutmentis adjusted by the computer 16 in correspondence to the determineddeviation.

Finally, the abutment may also serve to control with the computer thedisplacement of the carriage part 3 and thus of the grinding wheels 11,12 when a circular disk is resting at the abutment instead of a templatewith the circumferential contour of the spectacle lens to be ground.

In all cases, the measurement of the circumferentially ground spectaclelens 24 can be performed on a very narrow abutment in the form of thering segment 23 when the spectacle lens 24 on the spectacle lens holdingshaft 14 is displaced in the axial direction according to its spatialcurve. This displacement in the axial direction can also be performedpurely mechanically, for example, with a Panhard rod.

Of course, a measurement of the circumferential contour of the lens 24can be performed already after pregrinding on the pregrinding wheel 11.This is advantageous because the pregrinding wheel 11 wears off fasterthan the fine-grinding wheel 13. Optionally, a further measurement ofthe circumferential contour can be eliminated completely after thefinish-grinding step. However, it is also possible to perform after thefinish-grinding step a measurement of the circumferential contour and tooptionally perform a further corrective grinding step.

Especially during measuring of the spectacle lens after thefinish-grinding step the speed of rotation of the lens holding shaft 14can be increased in order to be able to perform the measurement faster.For this purpose, via the computer 16 a control command can be sent tothe magnetic clutch 19 which reduces the pressure during measuringrelative to the pressure during grinding so that wear or forming oftraces on the ring segments 23, respectively, at the circumference ofthe spectacle lens can be avoided.

Of course, the invention can be used in an analogous manner also withspectacle lens edge grinding machines in which the grinding wheels canonly be rotated but are essentially stationary, while the lens holdingshaft can be radially and axially moved relative to the grinding wheels.

What we claim is:
 1. A spectacle lens edge grinding machine comprising:amachine frame; at least one grinding wheel connected to said machineframe; a rotatable spectacle lens holding shaft fastened to said machineframe, said spectacle lens holding shaft radially and axiallydisplaceable relative to said grinding wheel, wherein a spectacle lensis secured to said spectacle lens holding shaft for grinding with saidgrinding wheel; at least one abutment, connected to said machine framefor contacting a spectacle lens having been ground to have a desiredspectacle lens contour, wherein said at least one abutment comprises asensing head for measuring a spatial curve of the spectacle lenscontour; a transducer for detecting at least one actual radial value ofthe spectacle lens contour relative to said at least one abutment; acontrol device for controlling an axial position of said spectacle lensholding shaft together with the spectacle lens relative to said grindingwheel as a function of said spatial curve of the spectacle lens contour,wherein said control device is operative when said at least one actualradial value is measured; a computer for controlling said spectacle lensedge grinding machine, wherein said computer comprises a memory in whichnominal values of the spectacle lens contour are stored; wherein saidcomputer compares said at least one actual radial value to said nominalvalues in order to determine a deviation from said nominal values; andwherein said memory stores a programmable threshold value for saiddeviation and wherein said computer controls an additional grinding stepwhen said deviation surpasses said threshold value.
 2. A spectacle lensedge grinding machine according to claim 1, wherein said abutment is aring positioned laterally adjacent to said at least one grinding wheelso as to be stationary relative to said grinding wheel, wherein thespectacle lens after grinding the spectacle lens contour is transferredfrom a position at said grinding wheel to a position at said abutment.3. A spectacle lens edge grinding machine according to claim 2, whereinsaid ring is comprised of ring segments.
 4. A spectacle lens edgegrinding machine according to claim 2, wherein one of said rings ispositioned on either side of said grinding wheel.
 5. A spectacle lensedge grinding machine according to claim 2, further comprising astationary splash guard enclosing tightly said at least one grindingwheel exclusive a grinding zone for grinding the spectacle lens, whereinsaid rings are connected to said splash guard.
 6. A spectacle lens edgegrinding machine according to claim 1, wherein said at least oneabutment comprises a wedge-shaped groove for detecting said at least oneactual radial value of the spectacle lens, wherein lateral sides of saidwedge-shaped groove are positioned at an acute angle and wherein saidacute angle is identical to a maximum acute angle of a V-shaped bevel ofthe spectacle lens.
 7. A spectacle lens edge grinding machine accordingto claim 6, wherein said sensing head in addition to said wedge-shapedgroove has a plane area for determining said at least one actual radialvalue of a tip of the V-shaped bevel of the spectacle lens.
 8. Aspectacle lens edge grinding machine according to claim 1, furthercomprising a drive comprising an adjustable clutch for radiallydisplacing said at least one grinding wheel relative to said spectaclelens holding shaft, and further comprising a switching device acting onsaid clutch so as to reduce a transferred torque during measuring theactual value of said spectacle lens contour.
 9. A spectacle lens edgegrinding machine according to claim 8, further comprising a compoundslide rest connected to said machine frame, wherein said at least onegrinding wheel with said drive are connected to said compound slide restso as to be displaceable relative to said spectacle lens holding shaft,wherein said transducer measures a displacement of said compound sliderest within said machine frame relative to the spectacle lens contour.10. A spectacle lens edge grinding machine according to claim 1, whereinsaid transducer is a digital transducer.
 11. A method for grinding theedge of a spectacle lens with a spectacle lens edge grinding machine,said method comprising the steps of:a) measuring at least one actualradius of a predetermined angle at a peripheral point of a spectaclelens, ground to have a spectacle lens contour, relative to an abutment,wherein said actual radius is a radius of a circumferential V-shapedbevel of the spectacle lens and is measured relative to a wedge-shapedgroove of the abutment; b) inputting the at least one measured actualradius into a computer with a memory; c) comparing the at least onemeasured actual radius with a corresponding nominal radius stored in thememory of the computer to determine a deviation from said nominalradius; d) comparing said deviation to a threshold value stored in thememory of the computer; and e) controlling with said computer anadditional grinding step, when said deviation surpasses said thresholdvalue, for correcting the spectacle lens contour in order to compensatefor said deviation.
 12. A method according to claim 11, wherein in saidstep a) said actual radius is additionally measured relative to a planearea provided at the abutment, further including the step of comparingthe measured values measured relative to said wedge-shaped groove andrelative to said plane surface in order to determine whether acorrection of said deviation of the actual radius, measured relative tosaid wedge-shaped groove, is possible.
 13. A method according to claim11, wherein said step a) includes the step of rotating the spectaclelens at a rpm higher than the rpm for grinding the spectacle lens.
 14. Amethod for grinding the edge of a spectacle lens with a spectacle lensedge grinding machine, said method comprising the steps of:a) measuringthe actual radii of the entire spectacle lens contour of a groundspectacle lens relative to an abutment; b) inputting the measured actualradii into a computer with a memory; c) comparing the measured actualradii with corresponding nominal radii of the entire spectacle lenscontour, stored in the computer, to determine the deviations from saidnominal radii; d) comparing said deviations to a threshold value storedin the memory of the computer; e) averaging said deviations, when saidthreshold value is surpassed; and f) controlling with said computer anadditional grinding step based on said averaged deviations forcorrecting the spectacle lens contour.
 15. A method according to claim14, wherein said step a) includes the step of rotating the spectaclelens at a rpm higher than the rpm for grinding the spectacle lens.
 16. Amethod for grinding the edge of a spectacle lens with a spectacle lensedge grinding machine, said method comprising the steps of:a) measuringthe actual radii of the entire spectacle lens contour of a groundspectacle lens relative to an abutment; b) inputting the measured actualradii into a computer with a memory; c) comparing the measured actualradii with corresponding nominal radii of the entire spectacle lenscontour, stored in the computer, to determine the deviations from saidnominal radii; d) comparing said deviations to a threshold value storedin the memory of the computer; and e) controlling with said computer anadditional grinding step for correcting the spectacle lens contour suchthat only such areas of the spectacle lens contour are corrected inwhich the deviations surpass said threshold value.
 17. A methodaccording to claim 16, wherein said step a) includes the step ofrotating the spectacle lens at a rpm higher than the rpm for grindingthe spectacle lens.